Modular software possible or not recommended?

I'm coding a ERP software and I'm a big fan of modularity. However, I fear at one point it's no more useful. I have the following problem:

1. I could build one function, let's say Customer::remove(), wich contains code from Order::remove().
2. Or I could create Customer::remove() wich then access Order::remove()

Is it worth to use version 2 with this lot of overhead? I will need to create a new Object of type Order, build up a new connection in a thread, make a new transaction and return the result back from Order::remove() to Customer::remove() and analyse for possible errors.